1. Field of the Invention
The present invention relates to a method and a device for controlling a fuel-supply system.
2. Description of Related Art
From German patent application document DE 10 2005 023 700, a device and a method for controlling a fuel-supply system are known. In that particular fuel-supply system, a first supply unit supplies fuel from a reservoir to a second supply unit. At least a partial quantity of the fuel quantity supplied by the first supply unit is returned to the reservoir as return quantity via a return line.
In modern Diesel injection systems, the second supply unit, hereinafter also referred to as high-pressure pump, must be cooled and lubricated by fuel. This calls for a minimally required quantity of fuel, which is returned to the reservoir via the return line. Furthermore, the first supply unit, hereinafter also referred to as electric fuel pump, must convey the injected fuel quantity from the reservoir into the high-pressure pump.
For economic reasons, the electric fuel pump should supply only the absolutely required fuel quantity. If too much fuel is supplied, then this results in unnecessary fuel consumption. Furthermore, it leads to undesired heating of the fuel. For this reason, the supply quantity of the electric fuel pump is normally specified as a function of the operating state and the component tolerance system, in such a way that a desired fuel quantity is supplied. Moreover, the return quantities are used for keeping the reservoir filled, regardless of the fluid level of the tank, via active cup filling systems, e.g., a sucking jet pump.
To satisfy these requirements, the related art provides for a regulation of the pressure in the return line. The disadvantage of this related art is that the threshold value for the return quantity must be specified while taking large tolerances into account. This results in an unnecessary expenditure of electrical drive capacity in certain operating states.